The use of wood shuttering panels has always been very widespread in the construction sector, which panels provide multiple advantages, including that of providing good mechanical characteristics and nailability. However, wood shuttering panels have a short life due to the environment in which their activity is developed, since they are generally exposed to water, moisture, abrasive materials (cement, lime, concrete, etc.), which shortens their service life.
In addition, once deteriorated, they must necessarily be removed and the possibilities of repairing and recycling them are complicated and, in any case, limited.
The ecological impact involved in producing millions of square meters of shuttering panels from forest wood, as occurs with all products produced from an asset that is as scarce as wood, is not insignificant either.
For the purpose of the durability of the panel, shuttering panels combining wood and plastic materials have been developed for a long time. This type of panel is described in patents DE 19611413, DE 19611382 and EP 1 426 525. The wood panel is generally complemented with edges and borders of plastic materials, suitably assembled or fixed to the wood core, which prevent, to a certain extent, its deterioration in transport, falls and blows.
Likewise, processes for the production of panels formed only by polymeric materials, recycled rubber or combinations of various plastic materials have been researched and developed. This technology generally attempts to fulfill a dual objective, on one hand, dispose of the large amount of plastic waste generated by the automobile industry and search for a use for such waste through its recycling for the production of panels for construction.
A process for the production of panels from recycled materials is described in patent WO 2004/111368, which allows producing a composite board based on plastic and rubber from triturated tires. A core is obtained to which structural skins are added to complete the shuttering board. The board produced by this process is quite dense and difficult to recycle, in addition to not having good mechanical and nailability characteristics required of a shuttering panel.
Sandwich type isolated structural panels have been used for a long time, as described in U.S. Pat. No. 3,305,991, U.S. Pat. No. 3,555,131, U.S. Pat. No. 3,838,241 and U.S. Pat. No. 4,120,330. These patents develop the process for forming heat welded foams, preparing the foam inside a mold. There are many patents related to the foaming process for structural alignments such as a core of sandwich panels by continuous direct extrusion, using a physical type foaming agent. However, many of them are limited to the machinery necessary for producing the foamed panel, forgetting the formulation of the material used.
In addition, panels based on polymeric plastic materials such as polyethylene (PE) or polypropylene (PP) have been developed in the state of the art. PP has several advantages with respect to PE, such as its mechanical properties, the bending elastic modulus being 1.5 GPa for PP, and 200 MPa for PE. However, PP foaming has always been hindered because of its low extensional viscosity and shear viscosity in a molten state (melt-strength). This limitation, associated to the chemical nature of PP, means that the latter does not have in normal conditions enough melt-strength to withstand the expansion of the gas bubbles during the foaming process, causing the collapse of the entire cellular structure and considerably limiting the production of foams with a reduced density (<200 kg/m3). PP crosslinking processes by means of different chemical processes using catalysts were subsequently considered, providing the polymer with a higher melt-strength. However, in this case, due to the crosslinked structure of the polymer, even though light foams (<200 kg/m3) are produced, the recyclability and recycling thereof is an extremely difficult process.
On other occasions, installations have been developed for the production of sandwich materials using flexible polyurethane or polyolefin-based flexible foamed cores (LDPE, EVA . . . ) attached to the skins by means of adhesives, applied in footwear, sports, etc. An example is patent EP 1 745 909 A2.
Patent DE 2041892 describes an installation for making non-recyclable shuttering boards which contemplates the possibility of using a polyurethane foam core attached to the skins by means of using adhesives.
However, there is still a need in the state of the art to provide a panel for construction formed exclusively of highly durable, easily reparable polymeric materials which can be recycled and even be used as raw material for forming new stiff recyclable panels for construction when their useful life has ended, thus closing a circle which protects the environment and allows huge savings in scarce natural materials.
In this sense the inventors of the present invention have developed a formulation and a production and assembly lime which allows producing stiff sandwich-type structural panels to be applied in construction, having optimal features as shuttering panels, emphasizing their high stiffness, reduced density and long durability, in addition to being completely recyclable due to the absence of adhesives.